In recent years, the automotive lamp has been required to exhibit an improved appearance of the lamp chamber both when lit and unlit (i.e., when the lamp is on and off), as well as the original function as the lighting means. Among improvements of appearance, one of the biggest problems is an improvement of lamp color, that is, a hue exhibited by a lamp when observed from outside. For example, if a turn signal lamp (direction indicator) has its lamp cover (also called outer cover or lens) colored in yellow so as to emit yellow light (actually, amber color that is between yellow and orange, but called yellow for convenience) upon lighting, it is viewed and recognized as yellow not only under lit conditions but also under unlit conditions, and this may impair sense of unity and harmony depending upon the type or color of the vehicle. The problem of lamp color may become more complicated in the case of a rear combination lamp in which plural lamps are used in combination. For example, when a red stop and tail lamp (brake light, tail light), a yellow direction indicator and a colorless backup lamp (reversing light) are coexistent, it is always a problem how to achieve sense of unity and harmony in the color of lamp.
Although numerous attempts have been previously made to improve the sense of unity and harmony in lamp color, fully satisfactory result or practical success has not yet been obtained. For example, a method in which a colorless lamp cover is used and a yellow or red cap is attached to cover a light source in a lamp chamber, has been widely implemented. This method aims to obtain uniform colorless appearance under unlit conditions with differently colored light-emitting portions in a rear combination lamp. However, under unlit conditions, the color of a cap can be recognized through the lamp cover.
An automotive lamp is disclosed in Japanese Utility Model Registration Application No. 5-6510, in which, in order to mask the color of a colored cap under unlit conditions, a sheet having selective light transmissivity (semi-transparent mirror) is disposed between the colored cap and a lamp cover. However, this method has a serious disadvantage that light transmittance under lit conditions is also lowered. This method has another disadvantage that, for attachment of the semi-transparent mirror, manufacturing process becomes complicated, leading to increased cost.
Japanese Unexamined Patent Publication (Kokai) No. 5-290606 discloses a rear combination lamp in which light emitting surfaces of red, yellow and white are provided on an integrated lamp body, wherein a red inner lens is provided on the red light emitting surface, a yellow inner lens is provided on the yellow light emitting surface and a yellow green inner lens is provided on the white light emitting surface, while an outer lens of single red color covers each light emitting surface to obtain an integrated sense of a lens surface. With this method, however, unified appearance can be obtained only in red color under unlit conditions, and moreover, the outer lens is only faintly colored so that, undesirably, inner lenses disposed inside can be viewed and recognized. Thus, this method is unsatisfactory in the sense of unity. Further, with this method, manufacturing process is complicated for disposition of inner lenses, again leading to increase of cost.
Further, Japanese Unexamined Patent Publication (Kokai) No. 10-228812 discloses a lighting fixture for a vehicle comprising a housing, a bulb, a transparent colored cap covering the bulb, an inner lens with prism surface covering the cap, and an outer lens installed in the opening of the housing, wherein step-shaped parts are further formed on both front and back surfaces of a portion of the inner lens. With this method, however, manufacturing process is complicated due to complex construction of the lamp chamber and special processing of the inner lens, leading to increase of cost. Moreover, because the inner lens has a complex curved surface and prism pattern is coarse, the amber color of the cap is recognizable to some degree under unlit conditions, and this method has also a drawback that sense of unity is inadequate.
Another method that has been employed to improve the external appearance of the lamp chamber is a method in which the lamp cover is provided with a surface portion formed as a lens alternating with a surface portion not formed as a lens, so that the inner wall of the housing in the depth of the lamp chamber is visible through the surface portion not formed as a lens while the surface portion formed as a lens is recognizable mainly as its own surface, with the result that the feeling of the depth of the lamp chamber can be emphasized. In this method, however, the lamp cover is formed by injection molding, and therefore the lens pattern is so rough (with a pitch as large as one to several mm) that the pitches are seen as an eyesore.
Also, in order to improve the visibility of the rear turn signal lamps mounted at the corners of the vehicle body, a prismatic lens is often mounted on the cover surface. This improves only the functions but cannot improve the appearance. Further, the prismatic lens being formed by injection molding of a resin has a rough lens pattern and the pitches offend the eye.